The present invention relates, in general, to high frequency circuits and, more particularly, to passive elements of microwave integrated circuits.
Prior high-performance monolithic microwave integrated circuits (MMICs) have been formed on GaAs substrates in order to minimize signal propagation losses. Standard silicon substrates, although generally lower in cost to purchase, handle, and process than GaAs substrates, have not been used as high-performance substrates for MMICs because it has previously been believed that silicon is an unsuitable material for a such a circuit (which typically carries signals with frequencies greater than 500 MHz). Specifically, the lower resistivity of silicon relative to GaAs has been perceived as a significant disadvantage of the use of a silicon substrate. However, a MMIC that could use a silicon substrate would significantly reduce wafer and processing costs. Accordingly, it is desirable to have a MMIC that uses a silicon substrate, yet limits signal propagation losses to levels comparable to that attained with existing MMICs using GaAs substrates.